In part three of this series on citations between patent equivalents I took a closer look at European patent documents. What I found was that citation patterns for European documents are significantly different than what we find in the US. In fact, the importance of pre-grant applications is even more highly pronounced in Europe than it is in the US.
The previous post looked specifically at the US and found that not only did ~75% of all US patent documents from the collection studied have at least one forward citation associated with it but that in 60% of the cases where the granted patent did not have any forward citations the pre-grant application still did. The initial post on this topic started the discussion on whether patent equivalents should be counted together when considering citation counts. This post continues to generate a large number of comments in a variety of forums and has raised the issue of sources for patent citations and how they can vary. Looking more closely at citation sources is being considered for a future post.
To look at the situation with European patent documents and what the impact of patent equivalents would have on them I started with the same search strategy I used when looking at the US, all EP grants and applications with an application date between January 1st, 2004 and February 14th, 2004 and a corresponding publication year between 2004 and 2010. This generated 20,465 documents with 4,323 of them being granted patents. This is less than what I found for the same period of time in the US and the relatively small percentage of grants in the total set can be attributed to the additional pre-grant kinds associated with EP pre-grant applications.
Of the 4,323 granted patents only 273 or 6% of the documents had a forward citation associated with them. When compared to the 76% I found when looking at the US documents this was a significant difference. An argument can be made that this difference reflects the practice of the two offices when it comes to reporting citations from the examiners vs. the applicants since there is no requirement to provide known references when applying for a patent in Europe as opposed to the US.
What was interesting though is that when you look at the pre-grant applications associated with the European granted patents you find that 1,542 or 36% of these documents have at least one forward citation. While this is half as many as the corresponding situation in the US it appears that there is a propensity to cite European pre-grant applications as opposed to the granted patents. In the US the percentage of documents between grants and pre-grant applications was essentially equal but in Europe there is a much higher likelihood of finding forward citations associated with the pre-grant application than there is with the granted patent.
In the previous post I looked at the distribution of publication years for the total collection of grants versus the grants without any forward citations associated with it. In that case I wanted to make sure there was not a significant time since grant bias built into the collection. In the case of the European grants, since the percentage of the total with zero forward citations is so high, I decided to look instead at a comparison between the total grants and the grants with at least one forward citation. The chart below shows this comparison:
In the previous post I looked at the distribution of publication years for the total collection of grants versus the grants without any forward citations associated with it. In that case I wanted to make sure there was not a significant time since grant bias built into the collection. In the case of the European grants, since the percentage of the total with zero forward citations is so high, I decided to look instead at a comparison between the total grants and the grants with at least one forward citation. The chart below shows this comparison:
Looking again at the number of granted patents with at least one forward citation from this collection I found only 952 or 8% of the cases had them. While higher than the 6% I found for the initial collection with a four year publication year spread it is still significantly lower than what is found in the US.
Meanwhile, when looking at the corresponding pre-grant applications I found that 4,665 or 42% of the cases had at least one forward citation associated with them. Again this compares favorably to the 36% I found when looking at the earlier collection from a collection of publication years.
Finally, I looked at the number of cases where both the granted patent and the pre-grant application had forward citations associated with them. This, after all, was the question we started with, do pre-grant applications significantly impact the forward citation count of the corresponding granted patent when they are considered as equivalents. Of the 952 cases where the granted patent has at least one forward citation I find in this collection that 60% of the pre-grant applications also have forward citations associated with them.
There are three primary lessons that this study seems to provide:
It is clear from these examinations that working with patent citations can be complicated and it is essential to consider patent equivalents when representing this data.
